U.S. Pat. No. 4,381,830 discloses a continuous flow earmold tubing connector or continuous flow adapted (CFA) that connects sound conduction tubing from an ear hook of a hearing aid to an earmold that fits within a person's ear. The important feature of the invention disclosed in the patent is the diameter of the sound conduction passage in the connector or adaptor is the same as the internal diameter of the sound conduction tubing. This provides a smooth and continuous path along the sound-conduction tubing and the connector from the hearing aid to the earmold whereby the acoustical characteristics of amplified sound emanating from the hearing aid and traveling along the smooth and continuous path into the ear is not changed thereby resulting in improved amplified sound reaching the ear.
Whereas the CFA improves the amplified sound reaching the ear from the hearing aid, it is desirable to better shape the output and increase the gain from the hearing aid to achieve desired electroacoustic effects for persons wearing the hearing aids.